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/*
* Copyright (C) 2014-2016 Andreas Steffen
* HSR Hochschule fuer Technik Rapperswil
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*/
#include "ntt_fft.h"
#include "ntt_fft_reduce.h"
/**
* Described in header.
*/
void libnttfft_init(void)
{
/* empty */
}
typedef struct private_ntt_fft_t private_ntt_fft_t;
/**
* Private data structure for ntt_fft_t object
*/
struct private_ntt_fft_t {
/**
* Public interface.
*/
ntt_fft_t public;
/**
* FFT parameter set used as constants
*/
const ntt_fft_params_t *p;
};
METHOD(ntt_fft_t, get_size, uint16_t,
private_ntt_fft_t *this)
{
return this->p->n;
}
METHOD(ntt_fft_t, get_modulus, uint16_t,
private_ntt_fft_t *this)
{
return this->p->q;
}
/**
* Do an FFT butterfly operation
*
* x[i1] ---|+|------- x[i1]
* \/
* /\ w[iw]
* x[i2] ---|-|--|*|-- x[i2]
*
*/
static void butterfly(private_ntt_fft_t *this, uint32_t *x, int i1,int i2, int iw)
{
uint32_t xp, xm;
xp = x[i1] + x[i2];
xm = x[i1] + (this->p->q - x[i2]);
if (xp >= this->p->q)
{
xp -= this->p->q;
}
x[i1] = xp;
x[i2] = ntt_fft_mreduce(xm * this->p->wr[iw], this->p);
}
/**
* Trivial butterfly operation of last FFT stage
*/
static void butterfly_last(private_ntt_fft_t *this, uint32_t *x, int i1)
{
uint32_t xp, xm;
int i2 = i1 + 1;
xp = x[i1] + x[i2];
xm = x[i1] + (this->p->q - x[i2]);
if (xp >= this->p->q)
{
xp -= this->p->q;
}
if (xm >= this->p->q)
{
xm -= this->p->q;
}
x[i1] = xp;
x[i2] = xm;
}
METHOD(ntt_fft_t, transform, void,
private_ntt_fft_t *this, uint32_t *a, uint32_t *b, bool inverse)
{
int stage, i, j, k, m, n, s, t, iw, i_rev;
uint32_t tmp;
/* we are going to use the transform size n a lot */
n = this->p->n;
s = this->p->s;
if (!inverse)
{
/* apply linear phase needed for negative wrapped convolution */
for (i = 0; i < n; i++)
{
b[i] = ntt_fft_mreduce(a[i] * this->p->wf[s*i], this->p);
}
}
else if (a != b)
{
/* copy if input and output array are not the same */
for (i = 0; i < n; i++)
{
b[i] = a[i];
}
}
m = n;
k = 1;
for (stage = this->p->stages; stage > 0; stage--)
{
m >>= 1;
t = 0;
for (j = 0; j < k; j++)
{
if (stage == 1)
{
butterfly_last(this, b, t);
}
else
{
for (i = 0; i < m; i++)
{
iw = s * (inverse ? (n - i * k) : (i * k));
butterfly(this, b, t + i, t + i + m, iw);
}
}
t += 2*m;
}
k <<= 1;
}
/* Sort output in bit-reverse order */
for (i = 0; i < n; i++)
{
i_rev = this->p->rev[i];
if (i_rev > i)
{
tmp = b[i];
b[i] = b[i_rev];
b[i_rev] = tmp;
}
}
/**
* Compensate the linear phase needed for negative wrapped convolution
* and normalize the output array with 1/n mod q after the inverse FFT.
*/
if (inverse)
{
for (i = 0; i < n; i++)
{
b[i] = ntt_fft_mreduce(b[i] * this->p->wi[i], this->p);
}
}
}
METHOD(ntt_fft_t, destroy, void,
private_ntt_fft_t *this)
{
free(this);
}
/**
* See header.
*/
ntt_fft_t *ntt_fft_create(const ntt_fft_params_t *params)
{
private_ntt_fft_t *this;
INIT(this,
.public = {
.get_size = _get_size,
.get_modulus = _get_modulus,
.transform = _transform,
.destroy = _destroy,
},
.p = params,
);
return &this->public;
}
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